The coating industry is one of considerable importance in the industrialized world. It has ramifications extending in various technological areas. Hence, paints have been designed for the protection and decoration of masonry coatings, ferrous metals, nonferrous metals, wood substrates and the like. Also, paints have been designed to provide special properties to the surface on which they are applied. Examples include the pigmentation of anti-foulants, electrocoatings, flame resistant and intumescent paints, heat-resistant paints and fluorescent paints. Pigments have also been used to prepare inks and to color paper goods. Other examples of use of coatings include the pigmentation of rubbers, plastics, cosmetics, magnetic tapes, food, textiles, adhesives and ceramics.
With current technology, almost any type of coating composition prepared comprises binders, pigments and extenders which are combined to obtain the desired result. The most commonly used pigment is titanium dioxide. Titanium dioxide is insoluble in all liquids, with the exception of concentrated sulfuric acid and hydrofluoric acid. Titanium dioxide molecules produce a highly reflective white powder. The paint industry has by far the most widely diversified manufacturing requirements because each basic paint type such as flat, semi-gloss and enamel require different kinds and amounts of treatments using titanium dioxide. Still, titanium dioxide is used as a pigment by a large number of major industries such as paints, paper, plastics, rubbers, floor coverings, printing inks, ceramics, coated fabrics and roofing granules. All these industries have their specific requirements but the versatility of titanium dioxide has allowed adaptation of its use for various purposes.
Titanium dioxide produces the effect of whiteness on the human eye because it reflects all wavelengths of visible light to the same degree. Under red light, it appears red; under blue light, blue and under green light, green. Only under illumination containing all of the wavelengths of visible light does titanium dioxide appear white. This property coupled with the extremely high stability of the compound has led to its widespread use in the coating industry.
As a general rule, shades of color are obtained by mixing color pigments with black and white pigments. At the microscopic level, the white titanium dioxide pigments are very bright and their reflectivity is countered by the use of black pigments. This is generally how colors are made. Extenders in the form of ground powders having a particle size of usually 1 to 10 microns as well as binders which can be selected from a wide array of chemicals can be used to hold the pigments together to form an applicable composition.
However, the extreme stability of titanium dioxide, although an advantage from a technological point of view, is a serious drawback from an environmental point of view because any release of such a chemical in the environment can potentially create serious environmental hazards. The production of titanium dioxide causes the creation of massive amounts of highly toxic sulfur derivative by-products which are often released in the environment.
Beyond the environmental considerations is the fact that the use of strongly reflective pigments such as titanium dioxide in the production of colors can lead to problems when attempting to produce very specific colors such as those found in nature. In fact, the brightness of titanium dioxide makes it almost impossible to produce something other than colors of high reflectivity.